This invention relates to the production of a rare earth metal (lanthanide) salt of an organic acid.
Rare earth metal naphthenates, particularly neodymium napthenate, have use as part of the catalyst in the production of 1,4-butadiene rubbers. A number of methods are known for producing neodymium naphthenate.
One of these methods is the precipitation method. In this method, a water-soluble neodymium salt such as neodymium chloride reacts with a water-soluble naphthenate salt such as sodium naphthnate. The reaction takes place in an aqueous medium and the neodymium naphthenate is extracted into an organic solvent such as hexane. This method is cumbersome as the neodymium chloride is usually first prepared from neodymium oxide and the sodium naphtherate from sodium hydroxide and naphthenic acid.
Another method of producing neodymium naphthenate is by the direct reaction of neodymium oxide and naphthenic acid. The problem with this method is that high temperatures are required and that a viscous product is obtained. Also, it is difficult to avoid employing an excess of naphthenic acid.
In a further method solvent extraction is used whereby an aqueous solution of a lanthanide salt to which organic acids such as naphthenic acids or sulphonic acid have been added are extracted with organic solvents. As equilibria are quickly set up between the different components, this method has the disadvantage of low efficiency and low recovery of product.